Light emitting devices, such as Light Emitting Diodes (LEDs) or Laser Diodes (LDs), which use group III-V or group II-VI compound semiconductors, are capable of emitting light of various colors, such as red, green and blue, ultraviolet light and the like, owing to developments of device materials and thin film growth technologies. Moreover, these light emitting devices are capable of emitting white light with high efficiency through use of a fluorescent substance or color combination, and have advantages of low power consumption, semi-permanent lifespan, fast response time, safety and environmental friendliness as compared to conventional light sources, such as fluorescent lamps, incandescent lamps and the like.
Accordingly, application sectors of light emitting diodes are expanded up to transmitting modules of optical communication means, LED backlights to replace Cold Cathode Fluorescence Lamps (CCFLs) which serve as backlights of Liquid Crystal Display (LCD) apparatuses, white LED lighting apparatuses to replace fluorescent lamps or incandescent lamps, head lights of vehicles and traffic lights.
A light emitting device includes a light emitting structure disposed on a substrate formed of sapphire, for example. The light emitting structure includes a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer, and a first electrode and a second electrode are respectively disposed on the first conductive semiconductor layer and the second conductive semiconductor layer.
The light emitting device emits light having energy determined by an intrinsic energy-band of a material constituting the active layer in which electrons introduced through the first conductive semiconductor layer and holes introduced through the second conductive semiconductor layer meet each other. Light emitted from the active layer may vary based on the composition of the material constituting the active layer, and may be blue light, ultraviolet (UV) or deep UV, for example.
A light emitting device package includes a cerium-doped Yttrium Aluminum Garnet (YAG) phosphor. The phosphors are excited by blue light emitted from the light emitting device, thus generating yellow light. As such, white light may be created via mixing of yellow light and blue light.
Attempts have been made to replace the aforementioned YAG phosphor with a silicate phosphor or a nitride phosphor.
However, using the silicate phosphor alone may be problematic in terms of thermal stability. In the case of long-term use of the light emitting device package, the silicate phosphors are deteriorated by heat radiated from a light emitting diode, causing gradual luminance reduction.
In addition, using the nitride phosphor alone causes a lower luminous intensity than that of the YAG phosphor.
Deterioration of the phosphors and luminance reduction may result in luminance reduction and color discordance of a backlight unit, for example, using the light emitting device package.